They are predicting another brutal winter with a lot of snow. Looking back on the blizzard of 2010 when we received 22 inches in about 18 hours, it got me thinking about frost dates and growing zones.

Quick! What’s the difference between Growing Zone and Frost Free dates? If you know, go have a beverage, pat yourself on the back, and flip through a seed catalog. Everyone else? Read on!

Growing Zones refer to the lowest average temperature for a given location. For example, here outside Chicago, I am in Zone 5a, which means the lowest temperature I can expect is about -20F. Why is this important? It is useful when planting or growing perennials, as they are generally rated on hardiness based on lowest temperature tolerated. There are plants that grow perfectly well year to year in downstate Illinois that would never survive a Chicago winter. Knowing you zone is a handy tool for perennial gardeners.

Frost Free dates refer to the dates between the last frost (32F or 0C) in the spring or the first frost in the autumn. Generally the growing season falls between these two dates. Before the last spring frost you must have either planted frost tolerant plants or seeds or protected them in some manner. In the fall the same holds true, a freezing frost in autumn will kill any unprotected frost intolerant plants, ending the growing season. These frost free dates are also good guidelines to help you determine when to start your seeds indoors or when to set up plants in summer for a fall harvest. I’ve provided a handy tool for USA based gardeners. You’ll find it here: Frost Free Calculator. Keep in mind this information is based on 3o years of collected data. Your exact location may have a micro-climate so your experience may be slightly different. In dealing with mother nature we are looking at guidelines not absolutes!

I hope you find it useful. For my non USA readers, I am looking for the same data in Europe and other locattions. If you have a suggestion, please let me know!

Until next time, Keep Digging and Eat Well!